John Barnes Wrote: >I found > that a fair model for the ESL of a ceramic capacitor is to treat it as a > non-ferrous blob of the same size. From theory, the partial inductance > of a non-ferrous strap of length=L, width=W, and thickness=T is: > > ESL = (muv * L)/(2 * pi) * > [ ln(2 * L / (W + T)) +0.5 + (0.2235 * (W + T) / L) ] henries, > > where muv is the permeability of vacuum or about 1.257 uH/meter. > > So to a first approximation, when the thickness of the capacitor is > close to its width, the ESL will be roughly proportional to the > capacitor's length. > Hi John: Formulas for calculating ESL are interesting to me. I have also seen following equations published by Doug Brooks (in "ESR and Bypass Capacitor Self Resonant Behavior How to Select Bypass Caps", Page 4): C( i ) = (0.1 * ((0.01)^(( i-1 )/(nvalues -1)))) * 10^(-6) L( i ) = (10 * ((0.01)^(( i-1 )/(nvalues - 1)))) * 10^(-9) Where, i ranges from 1 to nvalues (number of capacitor values). A notable outcome is that the ratio of inductance L (in Henries) to capacitance C (in Farads) yields a simple constant: L( i )/C( i ) = [10 * 10^(-9)]/[0.1* 10^(-6)] = 10^(-8)/10^(-7) = 0.1 This implies (under those conditions when above relations are valid) knowing C allows calculating L. Examples. If C = 0.100 uF, then L = 10 nH; If C = 0.001 uF, then L = 0.1 nH. The equation you have given ( which relates ESL to capacitor dimensions ) and those by Doug Brooks ( relating ESL to capacitor value ) are useful; but also require understanding their application domains/limits. Is it correct to conclude that the only limitation/requirement to your formula is for the capacitor to be surface mount ceramic? Thank you . Abe Riazi ServerWorks ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu